Method and composition for non-squeal disc brake pads

ABSTRACT

A system is disclosed for removing squeal or noise from automotive disc brake assemblies. An emulsion of a normally soft polymer together with a cellulosic thickener, an anti-freeze compound, biocide and pigment is coated onto the back side of the outboard pad assembly. When dry the outboard pad assembly is mounted on an automotive disc brake assembly.

STATEMENT OF PROBLEM

It is well known to automobile businessmen and consumers alike, thatmany disc brakes emit noise or sequeals of various frequencies whenutilized. It has been found that the squeal or noise primarily occursnot because of the disc rubbing against the brake pad but insteadbecause the outboard pad assembly is often mounted to float suspendedbetween the disc and disc brake assembly.

The outboard pad assembly consists of a pad material, which makescontact with the disc and a support or mounting member, usually metal,upon which the pad is mounted. The outboard pad assembly upon brakingwill vibrate between the disc and brake pressure member. This brakepressure member may be the caliper housing or a part mounted internal tothe caliper housing.

The vibration emits squeals primarily because the support member isvibrating against the caliper or other internal parts. The vibrationbetween the disc and the pad material contributes insignificantly to thenoise problem. Most often the only solution offered by automobilemanufactures, parts manufactures and service people is to replace thepad assembly. Although a fresh pad may reduce the possible noiseemenating from the vibration between the disc and pad it does not attackthe much louder squeal problem due to vibration between the supportmember and caliper. Normally, after numerous pad changes, service peopleinstruct their customers that squeal is a built in characteristic ofdisc brakes and cannot be eliminated.

BRIEF SUMMARY OF THE INVENTION

The noise squeal problem has now been solved by damping the member thatsqueals. This is accomplished in the preferred embodiment by providing asystem in which the critical face dampens vibrations. A composition isapplied to the outboard pad support member which drys quickly to form asoft flexible film. This composition comprises an emulsion of a normallysoft polymer with a cellulosic thickener, a biocide, an anti-freezecompound and a pigment. This composition is allowed to dry on thesupport member for a few minutes and then the outboard pad assembly ismounted on the disc brake assembly.

DESCRIPTION OF DRAWINGS

Referring now to the drawings,

FIG. 1 is a sectioned view of a typical disc brake assembly showing boththe inboard and outboard pad assemblies in addition to the rotor,caliper and piston assembly.

FIG. 2 is a front view of an outboard pad assembly along with theoutline of the caliper and rotor, illustrating the coating on the backside of the outboard pad assembly.

DESCRIPTION OF INVENTION

Referring now to FIG. 1, the caliper 10 of a disc brake assembly is thehousing member to which all parts necessary for disc brake operation isattached with the exception of the disc or rotor. An end view of thebrake rotor 12, which is commonly referred to as the disc is shown. Theoutboard pad assembly 13 contains a pad mounted on a support member. Theinboard pad assembly 14, is normally quite similar in size and shape tothe outboard pad assembly 13. The outboard pad assembly is secured tothe caliper 10 by using bolts 15, which normally secure the inboard padassembly 14 and outboard pad assembly 13 to the caliper 10. The mountingbolt 16 secures the disc brake assembly to the fixed steering assembly.A hydraulic line 17 is the passageway through which hydraulic fluidenters and moves the piston 18.

In FIG. 2, the outboard pad assembly 13 is more clearly shown with theback surface of the supporting member visible. The caliper 10, and disc12 are also shown. On the back surface of outboard pad assembly 13 isillustrated the coating of the soft flexible substance, referencenumeral 19, which is the essence of my invention.

More specifically, the above referenced composition contains a polymer.One such polymer is styrene butadiene rubber which is a standardsynthetic rubber. Any of several water base polymers with acceptableglass transition temperatures would be suitable. Specifically, oil inwater emulsions of acrylic and vinyl acetate copolymers, andterpolymers, acrylonitrile rubber, neoprene rubber, ethylene-vinylacetate polymers, polyurethane elastomers would be acceptable. A dryfilm which softens as measured by its glass transition temperature inthe range -40° C to plus 20° C is preferred to insure effective dampingof the vibrations. Its preferable to have between 40% and 70% of thepolymer emulsion to be solids. A composition with too low a solidscontent will not cover the surface as well as the preferred composition,and too high a solids content yields a composition which is difficult tospread.

A cellulosic thickener is used in the composition to create a paste-likeconsistency to the composition. It is desirable to obtain thispaste-like consistency for the purpose of ease of application by theoperator. In the preferred embodiment a Hydroxy ethyl cellulose which isa hydrophilic cellulose derivative is the thickener utilized. To achievethe recommended consistency 2-4% by weight of hydroxy ethyl celluloseshould be added. Other thickeners can be used, and in particular otherhydrophilic cellulosic thickeners such as, for example, carboxy methylcellulose are useful.

Ethylene glycol, a conventional anti-freeze may be added as afreeze-thaw resistant to insure that the composition reaches the user ina stable usable condition. Although ethylene glycol is presentlypreferred, the same freeze-thaw resistance may be obtained withpropylene glycol or a non-ionic surfactent. The composition alsoincludes a biocide to keep destructive bacteria and other causes ofdecay or deterioration at minimum development. Essentially any biocidethat kills off bacteria and mixes with the composition is satisfactory.In the preferred embodiment a product sold by Dow Chemical, Dowicil 75was utilized. An amount in the area of 0.2 parts by weight is sufficientto prevent bacterial growth.

A pigment is included in the composition, typically a thalo blue, whichis water dispersible for cosmetic as well as application reasons. Thepigments provides the operator applying the composition a method ofdetermining the areas already covered and the thickness of thecomposition on the covered areas. Although the color blue is preferred,any color sufficient to accomplish the above stated purposes isadequate.

This composition is used by applying a smooth coating to the backsurface of the outboard pad assembly. Once the coating is applied, it isallowed to dry for a short period of time. After the coating has dried,the outboard disc pad is mounted in the disc brake assembly in the usualmanner. The composition can be applied to the pad by the manufacturerand retains its effectiveness for many months, but for convenience ofshipping it is often preferred that the coating operation be carried outby the mechanic who actually installs the pad on the automobile.

I have found that when the composition is applied in this manner, itreduces squeal emanating from disc brake assemblies.

Therefore, I claim:
 1. A non-squeal automobile replaceable disc brakepad assembly comprising:a mounting member adapted to fit an automobilebraking system and for mounting against a brake pressure member of saidbraking system; a first surface of said mounting member beingpositionable against said brake pressure member, a coating on said firstsurface of a soft film polymeric emulsion having a glass transitiontemperature between the range of about -40° C and about +20° C; and abrake pad integrally mounted on one surface of said mounting member toface away from said brake pressure member and to be pressed against arotating disc braking member.
 2. A method of reducing squeal inautomotive disc brakes wherein said brakes include a brake padintegrally mounted on a rigid support member, said support member beingreplaceably mounted against a brake pressure member on automobilebraking systems to be pressed releasably against a rotaing disc memberand said support member, comprising;coating the surface of said supportmember at least on the surface positioned against said brake pressuremember with a permanently tacky polymeric rubber emulsion which, whendry, has a glass transition temperature ranging between about -40° C andabout +20° C, drying said coating; and mounting said pad and itsintegrally mounted support member on a brake pressure member of anautomobile braking system.